out neurotransmitters (chemical nerve messengers), and in digestive cells that send out digestive enzymes.
MITOCHONDRIAL PHYSIOLOGY Mitochondria have important physiological importance within the cell. These are responsible for the making of ATP molecules, which are the energy producing cells of the animal cell. ATP or “adenine triphosphate” is an adenine molecule with three phosphate side chains. There is energy stored in these phosphate molecules, particularly the third one. It takes energy to make an ATP molecule and, when it goes to make ADP plus phosphate, it releases energy that is used to drive many cellular processes. So, how is ATP made? There is a group of biochemical reactions done in and around the mitochondria that together make many ATP molecules. There are three basic processes in place to break down glucose, which is the main molecule metabolized in animal cells. In fact, all other substances (like amino acids, fatty acids, and others), are broken down into molecules that are a part of glucose in order to participate in metabolism. The first process actually takes place in the cytoplasm near the mitochondria. It is called glycolysis and breaks glucose down into pyruvate through several metabolic steps in order to make a few ATP molecules. These ATP molecules are, for the most part, used up in the participation of other metabolic reactions but this spending of energy later becomes necessary. Glycolysis is an anaerobic metabolism process because it doesn’t involve oxygen. The second process is called aerobic respiration because it involves oxygen. It takes the pyruvate made through glycolysis, brings it across the mitochondrial membrane, and involves the Krebs cycle or citric acid cycle. This makes more molecules of ATP and recycles many metabolites in order to do this. This happens inside the mitochondrion. The third process is called electron transport. It takes place across the membrane of the mitochondrion and makes the most ATP of any cellular process. Electrons are passed from one molecule to another and finally to oxygen, which accepts the electrons in order to make CO2 and water. The entirety of these three processes is called cellular
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